This invention relates generally to a method and system for reducing jet noise, and, more particularly, this invention relates to a method and system for jet noise reduction which can be selectively employed during noise sensitive portions of flight.
Exhaust jet noise is a major concern given the increasing demands on aircraft engines to reduce community noise levels. Jet engines produce reaction thrust by ejecting a high velocity stream of gas rearward from the exhaust nozzle or tail pipe of the engine. One of the problems of airplanes equipped with jet engines is that the exhaust stream creates a very high level of sound energy or “noise” in a wide range of frequencies, and a portion of this noise reaches the ground from low flying airplanes, as during takeoff and climb, at an energy level which is not acceptable to the public.
Mechanical chevrons are used in commercial engines to enhance mixing in the exhaust jet shear layer and reduce jet noise. Mechanical chevrons, however, have the disadvantage that they introduce losses in the engine cycle which persist for the entire duration of the flight beyond the noise-sensitive portions of the flight such as landing and take-off.